Through unyielding winds and icy rain, a long-legged, gray bird flaps its wings across the overcast Nebraska sky. Its squawk echoes an ancient call that has reverberated through this land for thousands of years. The bird is making its way to a dark cloud in the distance, one made of countless other birds—sandhill cranes, to be exact.

Each spring, roughly 600,000 sandhill cranes make their annual migration through Nebraska via the Central Flyway, a route also used by migrating ducks, geese, and shorebirds. The flyway is shaped like an hourglass stretching from as far south as Mexico to as far north as Siberia and cinched into an 80-mile-wide stretch in Nebraska. About 80 percent of migrating sandhill cranes congregate in parts of this cinch, where they reach their greatest density.

See thousands of migratory Sandhill cranes roost on the Platte River and feast on corn during their spring stopover in central Nebraska.

Their stopover in Nebraska’s Central Platte River Valley is considered one of the last great animal migrations on Earth. Although the cranes have been making the trek for generations, today, the prairie is threatened by human encroachment. Only 10 percent of the habitat is suitable for sandhill cranes, says Bill Taddicken, director of the Iain Nicolson Audubon Centre at Rowe Sanctuary in Gibbon. Agricultural use and urban development have stunted the once open and thriving grasslands along the river.

So far, the cranes have adapted, but it’s unclear how long their migration tradition can last if habitat loss persists. In recent years, a depleting ecosystem has forced them to stretch their migration eastward, which makes their commute slightly longer and more stressful. Conservation efforts seek to resurrect the struggling Platte River Valley so that the resilient fowl will continue their migration into the future.

“I think the four saddest words are, ‘You should have seen,’ and too often we have to say that,” Taddicken says. “And I don’t want my kid, or her kids, to ever have to say, ‘You should have seen the cranes on the Platte River.’”

Ancient Avians

At 1.2 metres tall, sandhill cranes are some of the biggest flying birds. (The endangered whooping crane can grow to 1.5 metres tall, and ostriches and emus are taller but earthbound.) Sandhills have heavy bodies layered with gray feathers that form a “bustle” over their back ends. They also have lanky legs, and long, curving necks that lead to heads topped with crowns of crimson feathers.

When the showy birds migrate through Nebraska today, they attract thousands of self-described “craniacs” from all over the world.

Taddicken says one of the characteristics that draws tourists to the ancient birds is their loud, rattling call. He adds that as cranes age, they go gray and bald, just like people. When they gather together on the Platte, they dance and exhibit behaviours that can only been seen at this stop.

En route to their northern breeding grounds, adult sandhills mate for life. After their offspring are born, they will care for them for a whole year, which is longer than most bird species.

Fossil records of sandhill cranes date back to the Miocene Epoch, some 10 million years ago, but they have been using the Central Flyway for only about 10,000 years. Before, they likely migrated over the Great Plains, but today they're attracted to the Platte's shallow, sandbar-filled channels, which are prime roosting turf. Each night during the migration, countless cranes gather en masse on the river, where they rest and stock up on protein-packed invertebrates and lizards.

With a good pair of binoculars, you can make out individual birds in the crowd. Some cranes perform an elaborate mating dance of wing-flapping, bowing, and jumping. Others crouch down and square off in a “ruffle bow,” or toss sticks and small prey up in the air. It’s like they’re getting together for a cocktail party, says Nicole Arcilla, avian ecologist and lead scientist at the Crane Trust in Wood River, or for a sleep-over.

“They are like us, except a better version,” Arcilla says.

When early settlers started planting corn, the birds took advantage. Today, Nebraska is an agricultural hub that thrives on maize, so during the day, cranes flock to farmers’ fields to feast on corn. This food helps them gain weight to sustain them for the rest of their flight, but it doesn't have all the nutrients they need—sandhills get 95 percent of their food from cornfields and the remaining five percent from the river.

“They can get some McDonald’s [from corn in the fields] but then they need to go to the health food store after,” says Andy Caven, habitat ecologist and lead biologist at the Crane Trust. “The prairie is sort of the Whole Foods store for cranes.”

Today, sandhill cranes’ population numbers are stable at more than 700,000 birds worldwide—about 80 percent make this annual migration. Although the general population is not listed as threatened or endangered, the birds’ non-migratory subpopulations in Mississippi and Cuba are endangered.

Biologists caution that further habitat loss poses a risk to the birds. The stretch of land the cranes flock to is shrinking and moving eastward, and the birds are coming earlier each year. These stressors can exhaust the birds, who already have to fly hundreds of kilometres each day during their migration.

SANDHILL CRANE MIGRATION - The Southeastern Arizona Bird Observatory is the place to see sandhill cranes. Some of these great birds migrate from as far away as Alaska and Siberia.

Although it’s unclear how climate change directly affects the cranes, it disrupts water resources. This unique river ecosystem is what draws the birds to the area, and a changing environment could jeopardise this.

"If the Platte disappeared they would have to adapt by finding another staging area [to fatten up] on their migration route," Arcilla adds. "Changing their migration route [now] would be much more difficult because their present journey is the product of thousands of years of evolution."

Saving a River “On Life Support”

Generations ago, early settlers referred to the Platte River, which flows from the Mississippi River via the Missouri River, as “1.6 kilometres wide and 2.5 cm deep.” Rushing water and ice jams from the Rockies used to scrape the prairies of sediment, creating for a network of sandbars and braided channels to spread out over the Nebraska plains.

But today, the ice jams have stopped scouring, and manmade dams starve the river of sediment. Planted trees, although helpful for geese, gulls, and eagles, are bad for shorebirds, says Caven, since they encroach on the river.

“It’s on life support, in a way,” Caven says. “Nebraska is probably the most intact [prairie] but that’s not saying much.”

Centuries of cycling drought and fire have shaped the Great Plains, where the birds used to migrate before they began reaping the benefits of the Platte. If the condition of the Platte keeps getting worse, Caven says, the cranes might scatter out. Decreased densities might still use Nebraska's wetlands, but there’s no telling, he says, and the species of other birds using the Central Flyway would change.

“The whole Platte is a particularly important area for pair-bonding and food acquisition,” Caven says. “And if we were to lose the habitat along the Platte, there’s really nothing of comparable size and quality to immediately replace it.”